Unidirectional fiber reinforced metal matrix tape

ABSTRACT

A UNIDIRECTIONAL FIBER-REINFORCED HETEROGENEOUS MATRIX TAPE HAVING SUPERIOR OFF-AXIS STRENGTH COMPRISING A PLURALITY OF HIGH STRENGTH, HIGH MODULUS FILAMENTS, A FIRST METAL MATRIX MATERIAL SUBSTANTIALLY ENCASING THE FILAMENTS AND A SECOND METAL MATRIX MATERIAL OF SUBSTANTIALLY HIGHER STRENGTH RELATIVE TO THE FIRST MATRIX MATERIAL BONDED TO AND IN LAMINAR RELATION WITH THE FILAMENTS AND THE FIRST MATRIX MATERIAL.

April 20, 1971 K. G. KREIDER 3,575,783

UNIDIRECTIONAL FIBER REINFORCED METAL MATRIX TAPE Filed NOV. 13, 1968 limited States Patent Oce 3,575,783 Patented Apr. 20, 1971 3,575,783 UNIDIREC'I'IONAL FIBER REINFORCED METAL MATRIX TAPE Kenneth G. Kreider, Glastonbury, IConn., assigner to United Aircraft Corporation, East Hartford, Conn. Filed Nov. 13, 1968, Ser. No. 775,246 Int. Cl. D04h 5/00 U.S. Cl. 161-143 6 Claims ABSTRACT OF THE DISCLOSURE A unidirectional fiber-reinforced heterogeneous matrix tape having superior off-axis strength comprising a plurality of high strength, high modulus laments, a first metal matrix material substantially encasing the filaments and a second metal matrix material of substantially higher strength relative to the first matrix material bonded to and in laminar relation with the filaments and the first matrix material.

The invention herein described was made in the course of or under a contract or subcontract thereunder, with the Department of the Air Force.

BACKGROUND OF THE INVENTION The present invention relates to the production of fiberreinforced composites and more particularly relates t the production of a unidirectional fiber reinforced metal matrix tape having substantial tensile strength in unreinforced directions.

It is known that fiber-reinforced metal matrix composites offer the potential of significant improvements in providing structural materials designed to meet the imposing requirements of space-age hardware. Potential advantages in utilizing a metal matrix rather than for example, a polymer matrix, are that metals have a better resistance to erosion or chemical attack at high temperatures, offer greater tensile, bearing, and shear strength and offer greater deformation prior to fracture. In the development of composites, it has been demonstrated that aluminum alloy matrices offer the best combination of strength to weight ratios, modulus to Weight ratios and resistance to fatigue and stress rupture. Several processes have been employed for the fabrication of aluminum matrix composites and include such techniques as molten metal infiltration, vapor deposition, electrodeposition, eutectic solidifcation and plasma arc spraying.

One of the paramount deficiencies in the production of unidirectional fiber-reinforced aluminum matrix composites has been their relatively low tensile strengths in unreinforced directions. It has #been demonstrated, for example, that at room temperature the tensile strength at 90 to the fiber axis of a boron fiber-aluminum matrix composite is lower than 20,000 psi., and at 45 to either fiber axis in a 0, 90 bidirectional reinforfement is lower than 30,000 p.s.i. At 600 F., the stress rupture properties of the same system result in failure at only 4,000 p.s.i. stress perpendicular to the fiber axis. In an attempt to remedy this problem, there have been substituted other matrix metals for aluminum with Vprincipal attention hav- Y ing been focussed on the metal titanium. Although titanium has a density which is higher than that of aluminum, it has a considerably higher strength at room and elevated temperatures and possesses other desirable attributes which make it attractive for use. Unfortunately, however the incorporation of titanium into a composite as a matrix component is fraught with difficulties and, until the present invention, so far as this inventor is aware, all attempts to effectively utilize titanium yas a matrix material have been unsuccessful in obtaining the predicted strength properties. The potential of consistently higher strengths in unreinforced directions through the use of titanium has thus remained unrealized and the actual strength and modulus to density ratios have been lower than those of the aluminum matrix systems. Primarily, the problem has centered upon the tendency of titanium, when being Ibonded into a composite, to either degrade the reinforcing fibers or to itself become embrittled, or both.

SUMMARY OF THE INVENTION The present invention relates to a composite having high strength, high modulus filaments and a heterogeneous matrix of metals combined in such a way as to more than double the strength in the unreinforced direction without the sacrifice of desirable properties. It contemplates the use of such filaments as for example, boron, silicon carbide, boron coated with silicon carbide (BORSICTM) and other suitable materials, and of a heterogeneous matrix in laminar form comprised of a relatively high strength material, as titanium, and a relatively low strength material, as aluminum or magnesium, to make tapes Iwhich are easily handled and highly reproducible. The use of aluminum, for example, as a bonding agent and matrix allows fabrication at lower temperatures and pressures and thus permits bonding and consolidation without degrading influences as evidenced hereinafter in a mechanical property evaluation. A number of the tapes are then preferably integrated into a multilayer composite.

In accordance with one aspect of the present invention, a multilayer composite is produced from a plurality of plasma sprayed bilayer tapes which are each fabricated on a titanium foil substrate under identical circumstances with respect to stress and temperature. A sheet of titanium foil is positioned on a mechanically expandable mandrel and a single filament is wound in helically collimated relation thereover. The filament is uniformly tensioned and preheated to a predetermined level and a metal matrix material is applied by plasma arc spraying. The intermediate monolayer tape thus produced possesses excellent bonding of the sprayed material to the foil and fiber with no signs of fiber degradation. The tapes are removed, everted and replaced on the mandrel and a repetition of the winding and spraying steps is enacted. The resulting bilayer tape is then removed and formed into a multilayer composite of the desired shape by consolidating a plurality of the bilayer tapes together and subjecting them to a hot pressing operation.

In another form of the instant invention, the monolayer tapes are removed from the mandrel and directly subjected, without the everting and additional winding and spraying steps, With other like monolayer tapes, to the hot press bonding operation.

By means of the present invention, not only is the production of structural high modulus composites attained, but the composites so produced are possessed of superior properties, particularly characterized by a great increase in strength in unreinforced directions. The article produced is extremely uniform and highly reproducible and the process by which it is manufactured is simple and relatively inexpensive. By virtue of the present teachings, a unique high-strength, high-modulus metal matrix composite is made available.

BRIEF DESCRIPTION VVOF THE DRAWINGS FIG. 1 is a side elevational view of a mandrel used during compohite fabrication;

FIG. 2 is a side elevational View, partly in section, of a plasma spray chamber; and

FIG. 3 is a cross-sectional view of a monolayer tape made according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like numerals indicate like parts, the numeral designates a hollow, cylindrical, diametrically split mandrel comprised of a pair of matching semi-cylindrical pieces 12 and 14. The mandrel pieces are secured together at their interface by a hinge 16 at one end and are pivotally separable to a controlled degree by means of a pair of springs 18 and a locking strap 20 located at the opposite end. The strap 20 is provided with a longitudinal slot 22 adjacent one end. A thumbscrew 23, having an enlarged head, is suitably received in the slot 22 and is operable to lock the mandrel in a spring-expanded position. The mandrel 10 has a central axial passageway 24 adapted for receipt of an appropriate driving shaft (not shown) so that the mandrel is both rotatable and axially movable.

According to the practice of the invention, with the springs biasing the pieces outwardly, the mandrel is locked in the open position and a sheet of titanium foil is laid in a single layer in covering relation over the entire cylindrical surface thereof in a smooth and uniform manner. Filamentary material is selected and wound in closely laid, evenly spaced helical convolutions on the foil. This can be accomplished by drawing continuous filament from a supply reel, securing the end of the filament adjacent the side of the mandrel, and guiding the lament under winding tension, by suitable payoff means while the mandrel is rotated. The exact mechanism by which the ber is laid on the foil substrate is not considered part of the present invention and those skilled in the art `will recognize that there are a variety of schemes for placing filaments, in tension, on a mandrel in a collimated manner. By the term collimated is meant the state wherein adjacent liber lengths are evenly and uniformly spaced from each other and such a concept is equally applicable to a single fiber helically wound on the mandrel or a plurality of fibers wound on the mandrel and residing in parallel planes.

Upon completion of the winding, the filament is broken and affixed to the mandrel and the restraining strap 20 is released. The mandrel is then positioned in a plasma spray chamber 26 where deposition of the metal matrix material by means of a plasma torch 28 can be accomplished in an argon atmosphere. Prior to spraying, the mandrel, metal foil and wound filaments are preheated to a temperature sufficiently high to assure bonding to the matrix during plasma spraying. The actual heating 4 is accomplished both by infrared lighting and by the composition and flow rate of the plasma gas. Deposits were made Within a range of 400-500 amperes, 30-35 volts, and -160 cu. ft./hr. STP of argon. In addition to these variables, the deposit is affected by controlling the rate of powder feed, the position of the powder feed inlet hole of the plasma, the size distribution of the powder, the VYtorch to substrateY distance, the nature of atmosphere surrounding the plasma exhaust flame and the substrate, and the substrate temperature. Composites were made with a moderate feed rate with respect to saturation (3 pounds per hour of metal powder spray), the powder inlet located in the ionizing zone of the arc, 240 +400 mesh size spherical metal powder, a four to ve inch arc to substrate distance, an argon atmosphere, a substrate temperature of 400-600 F. and a relative velocity of the plasma spray arc across the substrate of two to eight inches per second.

The technique of preheating and plasma spraying not only causes the coalescent particles of matrix metal to encase the fibers and adhere to them, but at the same time causes the mandrel to thermally expand so as to operate against the bias of springs 18 and cause the mandrel pieces 12 and 14 to close. The mechanical contraction of the thermally expanding mandrel minimizes the Variations of tensile strain to which the laments would otherwise be subject. When the spraying is complete, the tape and the mandrel are cooled to room temperature and during the cooling process, the opposite compensatory mandrel action occurs. The thermally contracting mandrel is mechanically expanded by the action of the springs 18 so that the difference between the coefficients of thermal expansion of the bers and matrix is accounted for. In all, the fibers are subjected to not greater than 0.3% strain at spraying temperature.

After cooling, the tape is removed from the mandrel by cutting it transversely. The tape, having dimensions of the width and girth of the mandrel, is preferably made ready for remounting on the mandrel by subjecting it to a cleaning operation. The titanium foil is washed with a deoxidizer, such as a nitric acid-hydrouoric acid solution and then mounted on the mandrel with its foil surface facing outwardly. The ber winding, pretensioning, preheating and plasma spraying steps are then repeated so that there is formed a tape having a central base layer of titanium foil bonded on both sides to the plasma sprayed metal matrix and the high modulus, high strength bers.

Once the tape is removed, it is preferably subjected, along with other like tapes, to a secondary fabrication technique. In particular, the tapes are diffusion bonded together by hot pressing in a non-oxidizing atmosphere. The hot press diffusion bond is preferably done under conditions at which no continuous brittle intermetallic is formed, typically at 45 0-5 5 0 C. for one hour.

Various experiments were conducted to estabish the eficiency of the techniques hereinbefore described. During the investigations, an aluminum mandrel 6 inches wide and 20 inches in diameter was utilized. The mandrel was equipped with a pair of auto-valve springs, each having a spring constant of 900 1b./in. The strap 20 was operable to lock the mandrel at a maximum separation distance of 1A inch. Preferred fiber, matrix and foil materials suitable for use are set forth in Table I. It is to be understood that, as used herein, the word aluminum or the word titanium is a generic term which includes reference to the respective aluminum-base and titanium base alloys.

TABLE LPBEFERRED MATERIALS FOR COMPOSITE FABRICATION Fiber BORSIC l Diameter, inches-.0039-.0041 Modulus, p.s.i.-55-00 Average UTS, p.s.i. 25,000-500,000 Source-United Aircraft Research Labs.

1 Boron with .00010 to .00015 inch SiC coating. l 1.01 M Al i Si, balance Al.

6.0, o Al, 4.0% V, balance Ti.

Of course, although the above-listed materials have proven to be suitable, they do not represent an exclusive list. `Ihere are, of course, other materials which are suitabelfor use. An aluminum matrix of 1100 aluminum, for example, has proven satisfactory although not as superior as the 360 alloy. Other high strength, high modulus fibers which can withstand the temperatures of composite fabrication without deterioration or degradation can be used, as for example a boron fiber with a nitride surface. Finally, othe`r titanium foils which are compatible with the foregoing materials are useable, such as the allow comprising 2.5% Sn, 5.0% Al, balance Ti.

Considerable fabrication development was performed utilizing the fiber and foils listed in Table I in combination with the various aluminum powders. The mechanical properties of the resulting composites are set forth in Table II.

were hot pressed to form a composite having an average tensile strength of 130,000 p.s.i. parallel to the fibers and 30,000 p.s.i. perpendicular to the fibers. As shown in FIG. 3, the monolayer tape article produced according to the present invention comprises a titanium foil sheet 30, a plurality of aligned high strength, high modulus filaments 32 contiguous to the titanium sheet, and a matrix 34 of aluminum or magnesium encasing the filaments and bonded to the sheet and the filaments.

By virtue of the techniques herein described, there is produced a composite product which, because of its superior off-axis properties, can be used with unidirectional reinforcement under conditions which would necessitate multidirectional enforcement in an aluminum-boron or aluminumBORSIC system. It was determined however, that in order to develop the best high axial strengths and high tensile strengths at large angles to the fiber axis, the

TABLE II.-MECHANICAL PROPERTIES OF TITANIUM FOIL COMPOSITES Tested at 90 to fiber axis Modulus Volume Volume Plasma Tensile of elas- Strain percent percent spray strength, tici at Specimen No. ber foil alloy p.s 10 p.s i fracture 419-90 (average 5 tests)- l 35 21 360 39, 800 12. 0 0.035 553 3G 31 6, 061 62, 000 i582 (averagel 6 tests) 42 16 2, 024 25, 200 14. 5

Tested at 0 to fiber axis 1553 3e 31 e, 061 154, ooo o. 0055 419A (average 2 tests) 42 19 360 122, 000 31. 5 0. 0037 419B (average 5 tests) 36 21 360 104, 000 29. 9 582 (average 6 tests) 42 16 2, 024 157, 000 31. 3 0.0057

l Bonsro NOTE: Specimen 553 utilized the 4911 foil while the other specimens utilized the C. P.

Titanium ioil.

In one investigation, tapes were fabricated by winding BORSIC fiber (nominal diameter 4 mils) on a foil of 4911 titanium 2 mils thick. 6061 aluminum was plasma sprayed from a powder 37-l00y. in diameter at 18 kw. and 160 cu. ft /hr. NTP argon. The substrate temperature was 250 C. at 5 inches from the plasma head. The composition of the tape, by volume, was 33% 4911 foil, 33% 6061 aluminum and 34% BORSIC. A plurality of tapes were hot press diffusion bonded at 550 C. at 6000 p.s.i. in argon to form an eight layer unidirectional ber composite having 154,000 p.s.i. average tensile strength parallel to the fibers and 62,000 p.s.i. average tensile strength perpendicular to the fiber axis. At 300 C., the average tensile strength perpendicular to the fibers was 49,000 p.s.i.

In another investigation, tapes were fabricated by winding BO-RSIC fiber on a foil of commercially pure titanium one mil thick. 2219 aluminum was plasma sprayed from a powder 37-100n in diameter at 18 kw. and 160 cu. ft./hr. NTP of argon. The substrate temperature was 250 C. at 5 inches from the plasma head. The composition of the tape, by volume, was 18% Ti foil, 42% 2119 aluminum, and 40% BORSIC. A plurality of such tapes composition should fall within the following ranges, by volume: 30-50% fiber, 1035% Ti foil and 30-50% aluminum matrix. Further, it has been found that best results obtain when, while working within the above ranges, there is maintained at least (by volume) as much aluminum as there is fiber.

In the practice of the present invention, it is recognized that modifications can be made. For example, plasma spraying can be performed in air. The properties of composites sprayed in air are found to be nearly equivalent to those fabricated in an argon atmosphere.

It will readily be seen that, through the use of the techniques hereinbefore described, fiber-reinforced articles of remarkable olf-axis strength can readily and reproducibly be fabricated. While the invention has been described with reference to specific examples, fabrication parameters and materials, these embodiments and conditions are intended to be illustrative only. Various modications and alternatives, other than those already mentioned, will be readily evident to those skilled in the art within the true spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

1. A unidirectional filament reinforced composite material capable of withstanding substantial stress in a direction normal to the filament axis comprising a sheet of titanium, a plurality of aligned high strength, high modulus filaments contiguous to said titanium sheet, and a relatively low strength matrix of aluminum or magnesium encasing said filaments and bonded to said sheet and said filaments.

2. The invention of claim 1 wherein said matrix is aluminum.

3. The invention of claim 2n wherein said matrix is comprised of coalesced particles of plasma sprayed aluminum.

4. The invention of claim 3 wherein said tape has a composition, by volume, of Sil-50% filament, 10-35% titanium foil and Z110-50% aluminum matrix.

5. The invention of claim 4 wherein said filaments are comprised of a material selected from the group consisting of boron, silicon carbide and silicon carbide coated boron.

UNITED STATES PATENTS 3,466,219 9/*1969 Schwartz 161--143X 3,473,900 10/1969 Sara 29--198X 3,471,270 10/1969 Carlson 29191.4

PHILIP DIER, Primary Examiner U.S. Cl. X.R.

161-207; ll7-93.1, 105.2; 29-19l.4, 191.6, 198; 156-171 

